Unit: Optics
Year: 1993 Question#: 92
Question: The diagram below represents a convex (converging) lens with focal point F.
If an object is placed at 2F, the image will be
(1 ) virtual, erect, and smaller than the object
(2 ) real, inverted, and the same size as the object
(3 ) real, inverted, and larger than the object
(4 ) virtual, erect, and the same size as the object
What is this question really asking?
Explanation by: David V
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Answer 1
virtual, erect, and smaller than the object
INCORRECT
When an object is placed outside of the focal length of a converging lens, the image is real, not virtual. Also, an object placed outside the focal length of a converging lens creates an inverted image (see diagram.)
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Answer 2
real, inverted, and the same size as the object
CORRECT
See diagram.
The image is real because the object is placed outside the focal length of a converging lens. Using congruent triangles, we see that AB = CD, thus the image is also the same size as the object. return to top
Answer 3
real, inverted, and larger than the object.
INCORRECT
See diagram.
The object is real and inverted, but we can see through congruent triangles that AB=
CD, which means that the image is the same size as the object.
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virtual, erect, and the same size as the object.
INCORRECT
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